Chemistry and Chemical Biology ETDs

Chuan Chen

Publication Date

5-3-1979

Abstract

A new method for determining ultrasonic velocity and its appli­cation as a high-performance liquid chromatography (H.P.L.C.) detector ·is developed. The method involves in using a three­transducer phase-shift device where two transducers alternately transmit ·1-MHz continuous wave signals to the same receiver. Ultra­sonic velocity can be calculated from the phase-shift difference between the two cell paths. When the device is used as an H.P.L.C. detector, the reciprocal of the phase-shift difference between the two cell paths is converted to an electrical signal and recorded on a chart paper with respect to retention time. The theoretical principles are discussed and the appropriate equations are derived.

Two independent sets of instruments are designed and utilized in the st1udy. The first generation instrumentation is used to examine the three-transducer method. An improved set of instrumentation was then constructed for use as an H.P.L.C. detector as well as; an ultrasonic velocity measuring device. The instruments and the associated electronics are illustrated and described in detail. An operation manual of this device is included as an appen­dix. The construction and dimensions of the solution cells are illustrated in figures.

The relationship between ultrasonic velocity and solution con­centration was studied in aqueous electrolyte solutions and alcohol­water mixtures. The results obtained from velocity measurements show a precision of± 0.2 percent with the first generation instru­ment and of ± 0.01 percent with the improved device. This corres­ponds to a1bout = 0.15 meter/sec for ultrasonic velocity in water. As an H.P.L.C. detector, the improved device results in an overall detector sensitivity of 0.25 µmole, a combined long and short term noise of 0.1 mV, linear dynamic range of about 2.2 orders of magnitude,, and better than± 2.5 percent short term reproducibility (mostly injection error). Because the cell volume is quite large (0.5 ml), the detector sensitivity and the low end of linear dynamic range may be improved several orders of magnitude by reducing the cell volume to the micro liter range. Because of the temperature sensitivity, the cell assembly has to be thermo-statted to better than 0.1°c. As a universal H.P.L.C. detector, this device will have a unique property -its temperature dependence is negligible when binary mixtures at certain compositions are used as the mobile phase.

Language

English

Document Type

Dissertation

Degree Name

Chemistry

Level of Degree

Doctoral

Department Name

Department of Chemistry and Chemical Biology

First Committee Member (Chair)

Edward A. Walters

Second Committee Member

Roy Dudley Caton Jr.

Third Committee Member

Nicholas Ernest Vanderborgh

Fourth Committee Member

Milton Kahn

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